U.S. regulators have approved use of a powerful Johnson & Johnson antibiotic to treat plague, an extremely rare, sometimes-deadly bacterial infection. The Food and Drug Administration also approved Levaquin, known generically as levofloxacin, to reduce risk of people getting plague after exposure to the bacteria that cause it. Called Yersinia pestis, the bacteria are considered a potential bioterrorism agent. Plague mainly occurs in animals. People can get it from bites from infected fleas or contact with infected animals or humans. About 1,000 to 2,000 human cases occur worldwide each year.